Mechanical systems (engines, transmissions) utilize a lubricant (oil) to dissipate heat within the system and to reduce wear on system components. However, due to the nature of the systems, wear does occur, resulting in the presence of metallic flakes or particles in the oil.
Due to the normal wear and to the natural breakdown of the oil, the oil in such systems must be changed periodically. This is typically done on a time or usage basis, for example, every 90 days or 2000 hours of use. The metal particles may be a result of this normal wear, but may also be an indication of abnormal wear or a more serious problem. For example, if the gears within a transmission are not meshing properly, the resulting wear creates abnormal amounts of metal particles within the lubricant. Under normal maintenance procedures, the metal particles would be present in the lubricant for an extended period of time. If this condition is not identified and the appropriate repairs completed, more expensive repairs, including the replacement of major system components, may result.
U.S. Pat. No. 4,323,843 issued Apr. 6, 1982 to Ian N. Batham discloses an apparatus for detecting ferrous contamination in a fluid. A similar device is available from the Komatsu Dresser Company of Peoria, IL under the name Metalert. As shown in, FIG. 1, the apparatus 100 of Batham includes a magnet 102 having north (N) and south (S) poles and first and second electrodes 104,106. The electrodes 104,106 are parallel to the plane formed by the magnet poles, N,S. A spacer 108 electrically isolates the two electrodes 104,106 from each other.
In operation, the electrodes 104,106 and the spacer 108 form a plug which is inserted into a container containing fluid. Ferrous particles are attracted into contact with the two electrodes 104,106 by the magnetic field generated by the magnet 102. The resistance between the two electrodes is measured as an indication of the particles.
There are however several inherent problems with the Batham design. For instance, the sensor design does not protect the particles already attracted to the sensor from currents within the oil. Therefore, particles are continually being "swept" away by the currents. The result is a "noisy" or unstable sensor output. Furthermore, the sensor design does not allow for detecting non-ferrous electrically conductive particles. In some systems, certain system components consist of nonferrous metals, for example, aluminum, brass or bronze. Since the Batham design relies solely on the magnet to attract particles, these types of harmful particles would not be detected.
Furthermore, magnetic particles are more strongly attracted to the top surface of the bottom electrode 104 because it is closer to the magnet. In order for the resistance across the electrodes to change, the particles must "pile up" in order to bridge the gap.
U.S. Pat. No. 2,462,715, issued Sep. 16 1944 to James C. Booth discloses a sensor having two magnetic members connected to a plug. The magnetic members face each other and extend away from the plug into the fluid. This arrangement also has several limitations. First, as in the Batham design, the particles trapped within the sensor may be "swept" away by currents within the fluid. Secondly, since particles are in direct contact with the magnetic members, the particles are not so easily removed for cleaning when the oil is changed.
The present invention is directed to overcoming one or more of the problems, as set forth above.